This invention relates to sprockets for abrasion resistant drag-type feed chains such as commonly employed in feeding comminuted materials to processing vessels in chemical, metallurgical and other processing industries which are particularly resistant to high temperature, corrosive environments.
In certain industries, it is necessary to feed granular or comminuted materials to processing vessels such as furnaces, reactors and the like. Sometimes it is possible to feed these materials to such equipment by means of screw conveyors, belts, and other conventional solids-handling apparatus. However, in certain instances, particularly where the solid material is highly abrasive and also where high operating temperatures and corrosive atmospheres are encountered, it is necessary to employ so-called "drag chains." Such drag chains are typically endless belts formed by interconnecting metal links which are specially constructed to withstand the severe conditions encountered. For example, such drag chains are commonly employed to feed concentrates or calcined ores to the reverberatory furnaces in copper smelters.
The dry materials, either concentrate or calcined ore, are fed to the reverberatory furnace in a modern copper smelter through relatively small ports located in the ceiling of the furnace. These ports are spaced along the sides of the furnace at appropriate locations to form piles of the solid material along the walls of the furnace. These piles melt at their base and are continually replenished by the addition of further solid material at the top of the pile. Drag chains are employed to transport the solid materials from their storage point along channels in the feeding ports in the ceiling of the furnace. The drag chains are almost constantly subjected to the very corrosive gases produced in the furnace and are further subjected to high temperatures from the furnace itself and from the hot solid materials being fed to the furnace. This combination of corrosive atmosphere, high temperature, and abrasive material being handled presents a serious maintenance problem, necessitating frequent repair and replacement of the drag chain and the sprockets on which they are carried.
In the case of the typical sprocket construction the wear of the sprocket is further aggravated by the build-up of the abrasive materials between the sprocket and the chain. Because of the normally closed or solid construction of the sprocket, the entrapped material has no free avenue of escape, and as it collects it interferes with the normal operation of the sprocket and chain.
While the replacement of the chain is costly in terms of lost operating time for the equipment, the replacement of the sprocket represents an even greater expense because it typically involves a relatively more complete disassembly of the equipment. For this reason the teeth are sometimes designed to be removable from the main sprocket assembly to permit replacement of the teeth without removal of the main body of the sprocket. Because the cost of the teeth is significant in itself, it is important that the design of the sprocket and teeth should take this factor into account and should provide for long life and minimum cost also for the teeth.